As Congress presses the Obama administration to adopt a more aggressive posture toward Iran, the U.S. government is stepping up its efforts to isolate Iran from the international banking system.

On Tuesday, Attorney General Eric Holder and Undersecretary of the Treasury Stuart Levey announced a half-billion-dollar settlement with Credit Suisse, which admitted to criminal violations of U.S. sanctions on Iran. Its scheme, Holder said, was “decades-long.”

“At one point,” Holder said, “the company even developed a pamphlet for its Iranian clients, explaining how to fill out payment messages so as not to trigger U.S. filters. They created a ‘how-to’ book on committing a crime — and it worked well for years.”

The action “is the most effective thing that’s been done on Iran, more than [United Nations] sanctions, even more than the formal Treasury sanctions,” said Michael Jacobson, a former senior adviser to Levey at the Treasury Department’s Office of Terrorism and Financial Intelligence. Levey has “gone out to the private sector and convinced them that it is not in their interest to be doing business with Iran.”

But along with this effort to further isolate Iran, the Obama administration announced another measure designed to open up communications there. That seemed the intent of the State Department’s notification of Congress this week that it was authorizing the Treasury Department to relax restrictions prohibiting Iranians from downloading free American software such as Twitter and Google shown to be in prominent use in the run-up and aftermath of Iran’s disputed June 12 elections.

Meanwhile, on Monday, the House overwhelmingly passed a bill that would ban foreign entities from selling refined petroleum products or refinery equipment to Iran.

The House bill would sanction foreign companies that sell refined petroleum to Iran or help Iran with its own domestic refining capacity by depriving those companies of access to the U.S. market.

At issue for the administration is whether the president will have the discretion to be able to impose sanctions, or, as required by this bill if it becomes law, be required to impose the sanctions or seek a waiver in each case he would not.

More broadly, the legislation raises the question of how much flexibility the Obama administration will have to try to continue pursuing a complex international diplomatic strategy on Iran or how much Congress will seek to essentially force the administration to take a more aggressive unilateral approach.

Speaking after his bill passed Monday, Rep. Howard Berman (D-Calif.), chairman of the House Foreign Affairs Committee, said he believed his bill would empower the Obama administration’s Iran policy efforts, not force its hand.

“The administration did not say, ‘Go ahead,’ and they did not tell me not to go ahead,” he acknowledged. “And I have been as transparent as I could be with them.”